You can use somebody else’s PS4 from your PS4

At the Sony PlayStation Meeting, it was revealed just to watch extent Gaikai streaming technology will be integrated into the PS4.
In addition to streaming games from the cloud, the PlayStation 4’s use of Gaikai streaming will allow for a gamer in her home reach into the console of her friend around the world and play on his console. The example of a use for this is if you need help getting through a tough section of a game, you can call your friend for help and she can take over for you from where she is. Presumably there will be other uses for this.